       Re: the ellipse and the circle

• To: mathgroup at smc.vnet.net
• Subject: [mg69219] Re: the ellipse and the circle
• From: Urijah Kaplan <uak at sas.upenn.edu>
• Date: Sun, 3 Sep 2006 01:39:02 -0400 (EDT)
• Organization: University of Pennsylvania
• References: <200609011041.GAA25668@smc.vnet.net> <edadmf\$pef\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```After using those options, try using FullSimplify[Reduce[]] instead of
Solve[] on your equations, and see if you like the form of those answers.

--Urijah

>
> Your equations are equivalent to finding the roots of a 4th order
> polynomial. By default, Solve will use radicals to express the root of a
>   quartic polynomial, and hence yields an enormous and useless result in
> this case. We can control this behavior by changing the options of Roots:
>
> SetOptions[Roots, Cubics -> False, Quartics -> False]
>
> Now using Solve will produce much smaller results at the cost of
> containing explicit Root objects.
>
> Carl Woll
> Wolfram Research
>
>> In:=
>> \$Version
>> Out=
>> "5.1 for Microsoft Windows (October 25, 2004)"
>> In:=
>> e = x^2/a^2 + y^2/b^2 == 1
>> Out=
>> x^2/a^2 + y^2/b^2 == 1
>> In:=
>> x0 = a*Cos[\[Theta]]
>> Out=
>> a*Cos[\[Theta]]
>> In:=
>> y0 = b*Sin[\[Theta]]
>> Out=
>> b*Sin[\[Theta]]
>> In:=
>> c = (x - x0)^2 + (y - y0)^2 == r^2
>> Out=
>> (x - a*Cos[\[Theta]])^2 + (y - b*Sin[\[Theta]])^2 == r^2
>> In:=
>> Solve[{e, c}, {x, y}]
>>
>> [thousand of lines deleted]
>

```

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